A common folding bicycle has only one folding joint on its beam, by which the bike frame can be folded laterally so that the front and rear wheels can be put together. As shown in FIG. 1, after the bicycle is folded, the frame sticks out and the bicycle is still too bulky for packing and carrying. As shown in FIG. 2, in a folding bicycle disclosed by a UK patent, a folding joint is installed on its beam and the rear fork is hinged with the frame, so that the front part of the bicycle can be folded laterally via the folding joint and the rear fork can be folded forward around the hinge axle 6a. As shown in FIG. 3, since this bicycle can be folded at two points, after the bicycle is folded, the frame is positioned between two wheels instead of sticking out, and the folded bicycle is smaller in volume. However, since the hinge axle 6a is parallel to the central axle 7a, after the bicycle is folded, the rear wheel 8a is positioned below the beam 3a. As a result, the beam is slightly higher than the wheel. Meanwhile, the beam must be humped up in order to have the rear wheel placed under it, which looks not natural and orderly, and which affects the strength and rigidity of the folded bicycle. Furthermore, since the hinge axle is parallel to the central axle, the rear part of the bicycle can not be folded sufficiently close to the beam and the bicycle still has a large width after being folded.